1. Field of the Invention
The subject invention relates to material feeding apparatus and, more specifically, to rotary transfer valves and rotary feeders, including apparatus for transferring material between different environments, including different pressure zones.
2. Prior Art
Rotary feeders and related apparatus are well known as may, for instance, be seen from U.S. Pat. Nos. 3,913,800, 3,895,745, 3,603,001, 3,231,105, 3,201,007, 3,077,272, 3,052,383, 2,984,872, 2,907,499, 2,888,175, 2,886,191, 2,879,094, 2,858,212, 2,806,636, 2,367,311, 1,215,531, 1,143,634, 659,086, 627,498, and U.S. Pat. No. Re. 26,275.
Existing rotary feeders with fixed, rigid blades tend to leak as their rotor blades or cavity walls wear in service. Rotor replacements or adjustments are time consuming and expensive and cause considerable down time of the equipment.
In many instances, material accumulates in the rotor pockets of the feeder and is difficult to remove without shutting down the installation. Such accumulating material gradually diminishes the capacity or throughout of the feeder and renders the same eventually useless. Present dislodgment techniques are not very effective; typical being the dropping of balls contained in a hollow portion of the rotor hub.
With the advent of new industrial processes which require abrasive solid materials to be handled at high temperatures, high pressures and high differential pressure between inlet and outlet, existing rotary feeder equipment is no longer adequate for continuous operation. Clearances between the rotor and the housing to compensate for thermal expansion become critical, and tend to cause seizure between the rotor and the housing. If these clearances are too large from initial seizing or wear, an inverse pressure results by air leaking between the rotor and housing in such quantities that it fluidizes the material in the inlet with resultant interrupted flow of material into the rotor pockets. Existing techniques provide flexible or adjustable tips on each blade in an effort to overcome the latter disadvantages. This, however, renders the construction more complex and expensive.
The present invention resides in a rotary feeder comprising, in combination, means including a housing for providing a cylindrical cavity having a longitudinal axis, an inlet issuing into a first peripheral portion of the cavity, an oulet interconnected with the cavity through a second peripheral portion circumferentially spaced from the first peripheral portion, the maximum dimension of each of the inlet and outlet parallel to the longitudinal axis being smaller than an axial dimension of the cylindrical cavity; means for successively transporting material from the inlet to the outlet through the cavity including a valvular rotor in the cylindrical cavity having a hub; means for mounting the hub for rotation about the longitudinal axis; means for defining a plurality of material-receiving pockets circumferentially distributed over the hub including rigid blades delimiting said pockets; means for mounting the blades for limited angular movement relative to the hub including axially extending recesses in the hub for receiving the inner edges of the blades and fixed projections extending outwardly from the hub adjacent to the recesses for supporting the blades, the blades having lateral dimensions extending in said cavity axially beyond the maximum dimension of each of the inlet and outlet and having widths from the recesses in the hub to the periphery of the cylindrical cavity greater than corresponding radii through inner edges of the blades at the recesses in the hub, whereby the blades are angularly inclined relative to the radii; wear compensating means on the fixed projections for applying outer edges of the blades opposite the inner edges to peripheral wall portions of the cylindrical cavity and for urging the blades angularly toward the corresponding radii to compensate for wear of the outer edges and the peripheral wall portions to maintain worn outer portions of the blades applied to or close to the peripheral wall portions of the cylindrical cavity; and means connected to the hub for rotating the valvular rotor in the housing. Wear compensating means include resilient means for biasing the blades toward the corresponding radii and gradually compensating for wear, and adjusting means for periodically moving the blades toward the corresponding radii to compensate for wear. The compensating means thus vary the inclination of the rigid blades relative to radii of the hub through the inner edges of the blade in the recesses of the hub.